The preferred embodiment concerns a method, a computer program and a printing system for trapping print data.
The preferred embodiment is related to other inventions that are described in German patent applications DE 10 2006 055 587.2, DE 10 2006 055 624.0 corresponding to U.S. Published Application 2008/0130028, DE 10 2006 055 625.9 and DE 10 2006 055 626.7. Their content is herewith incorporated by reference into the present specification.
Color documents or document parts (for example images, color graphics or the like) are for the most part described by image data that are organized in color separations. This type of data organization in turn corresponds to many print output methods or apparatuses that print the image data on a recording medium in color separations, for example in the colors yellow (Y), magenta (M), cyan (C) and black (K), or in black and one or more of what are known as highlight color colors or the Océ Custom Tone® colors.
The Assignee OCE Printing Systems GmbH develops and distributes corresponding digital electrographic printing systems. They are described in the publication “The World of Printers, Technologies of Océ Printing Systems”, Dr. Gerd Goldmann (Ed.), Océ Printing Systems GmbH, Poing, 7th edition (2002), for example. Various offset and digital printing technologies are described on pages 249-286; various digital color printing systems are described on pages 287-325; and the fundamentals of color printing are described on pages 233-248. The basics of digital image processing are described on pages 209-232. Principles of highlight color printing are described on pages 246-248.
A digital printing system for two-sided, monochrome and/or color printing of a recording medium is known from WO 98/39691. A method for preparing a pixel file in which contiguous regions of the image are determined from the pixels is known from the International Patent Application Nr. PCT/EP2004/00700 (publication number WO 2005/001765 A2).
Methods for trapping image data are known from U.S. Pat. No. 5,581,667, EP-A2-484 890, US 2003/0090689 A1 and US 2006/0033959 A1, U.S. Pat. No. 4,931,861, EP-A2-929 189, DE-A1-199 12 511, US 2001/0055130 A1 and EP-A2-833 216.
There is what is known as the passer problem both in digital printing and in offset printing. Such a problem is known wherein, given multiple printing processes on a sheet of paper, due to mechanical tolerances it cannot be guaranteed that the positioning of the paper in all printing processes is always exactly the same. The problem occurs in monochrome printing when the front and back side are printed separately, or given multicolor printing on one side.
This problem is disruptive given front-and-back side printing when, for example, a border is printed around the front and back sides and these borders do not lie exactly atop one another, which is noticeable when the page is held up to the light.
In multicolor printing the colors are offset relative to one another. As long as the different colors do not touch, this is not conspicuous. If the colors touch, due to the offset of the colors printed over one another at the contact line, this leads to an adulteration of the color impression, or a white gap (flash) remains at the contact line.
While the adulteration of the color impression is for the most part tolerable, the flashes (gaps) are extremely noticeable, as is shown by the comparison of exactly positioned colors in FIG. 1A and colors in FIG. 1B positioned with an offset.
To remedy the flash problem it is known to enlarge or to spatially overfill the brighter color. Although a greater overlap of the colors is therefore achieved, the flashes disappear, as is shown by the comparison of colors in FIG. 2A that are positioned with an offset and overlapped colors in FIG. 2B. Given the enlargement of an object, in the later printing process care must therefore be taken that the overlapping part is printed translucent since otherwise the problem is displaced to the border of the enlarged object.
The method just described that remedies this problem has the name “trapping” (overfilling). Trapping is offered in different products on the market. For example, it is a component of raster image processors (RIPs) of the page description language (PDL) Adobe PostScript® Level 3, the software SuperTrap® offered by Heidelberger Druckmaschinen AG or the software TrapWise® that is offered by Creo.
Trapping can be conducted in two different ways. Trapping can be dealt with at the object level or at the bitmap level.
In electrophotographic high-capacity printing systems the problem of trapping has previously been solved at the bitmap level (see for example WO 2006/069980 A1) since the print data can be automatically processed without delay at the bitmap level. Corresponding trapping methods can therefore be integrated into an electrophotographic high-capacity printing system without the printing operation being negatively affected by this. touch, due to the offset of the colors printed over one another at the contact line, this leads to an adulteration of the color impression, or a white gap (flash) remains at the contact line.
While the adulteration of the color impression is for the most part tolerable, the flashes (gaps) are extremely noticeable, as is shown in prior art U.S. Pat. No. 7,856,140 by the comparison of exactly positioned colors in FIG. 1A and colors in FIG. 1B positioned with an offset.
To remedy the flash problem it is known to enlarge or to spatially overfill the brighter color. Although a greater overlap of the colors is therefore achieved, the flashes disappear, as is shown in prior art U.S. Pat. No. 7,856,140 by the comparison of colors in FIG. 2A that are positioned with an offset and overlapped colors in FIG. 2B. Given the enlargement of an object, in the later printing process care must therefore be taken that the overlapping part is printed translucent since otherwise the problem is displaced to the border of the enlarged object.
The method just described that remedies this problem has the name “trapping” (overfilling). Trapping is offered in different products on the market. For example, it is a component of raster image processors (RIPs) of the page description language (PDL) Adobe PostScript® Level 3, the software SuperTrap® offered by Heidelberger Druckmaschinen AG or the software TrapWise® that is offered by Creo.
Trapping can be conducted in two different ways. Trapping can be dealt with at the object level or at the bitmap level.
In electrophotographic high-capacity printing systems the problem of trapping has previously been solved at the bitmap level (see for example WO 2006/069980 A1) since the print data can be automatically processed without delay at the bitmap level. Corresponding trapping methods can therefore be integrated into an electrophotographic high-capacity printing system without the printing operation being negatively affected by this.
However, the information regarding the objects is missing in dealing with the trapping at the bitmap level, whereby the trapping on the bitmap level is in principle significantly less efficient than the trapping at the object level.
The commercially available products indicated above—which are components of raster image processors (RIPs) of the page description language (PDL) Adobe PostScript® Level 3, the software SuperTrap® offered by Heidelberger Druckmaschinen AG or the software TrapWise® that is offered by Creo—generate additional trapping objects at the borders of the objects, which trapping objects reduce the effect of the passer problems. These additional trapping objects significantly increase the data volume of the corresponding print data file. In extreme cases, it can even increase the data volume tenfold since the number of individual objects can be multiplied. In these known solutions the trapping is executed interactively, such that an experienced user efficiently controls the generation of the additional trap objects depending on the sample to be trapped. However, these methods have proven themselves very well in offset printing, in which normally a great deal of time is available in order to correspondingly process the printer's copy before the printing process and to interactively conduct a trapping.
A method in which a trapping is executed in an electrophotographic printing is known from US 2003/017934 A1. In this method edge lists are produced from the objects, and objects that do not correspond to a predetermined shape can be divided up into corresponding standard shapes. Information of the objects is thus stored with the edge lists before the objects are rastered. The trapping itself occurs at the bitmap level, wherein the additional information of the objects are considered as well (for example in the form of the edge lists). The disadvantage of the trapping at the bitmap level (that information regarding the objects is no longer present) is thus somewhat reduced with this method. However, the generation of the edge list is complicated on the one hand, and multiple objects are additionally generated from single objects, which again makes the processing more difficult. Furthermore, the objects generated in such a manner are no longer identical to the original objects. Objects with complex shapes cannot be processed with this method, or can be processed only to a very limited extent.
A method for trapping of print data present in a print page language (PDL—Page Description Language) arises from U.S. Pat. No. 5,666,543. The print data are hereby initially analyzed, are supplied to a raster image processor (RIP), and trapping instructions are generated. The trapping instructions indicate whether the print data comprise text or graphics and whether they should be trapped using a shape directory in the RIP. The shape directory is generated in the analysis of the print data and transmitted to the RIP. The shape directory is a list of the shapes of the objects. The trapping regions or overfills are generated upon rastering in the RIP. This known method corresponds to the method known from US 2003/017934 A1, wherein the shape directory corresponds to the edge list.
The prior art can thus be summarized to the effect that there are on the one hand trapping methods that trap at the object level. However, these methods are not suitable to conduct the trapping in real time during the printing process in a digital electronic printing machine. These methods are primarily provided for offset printing, in which the image data is processed with an external raster image processor. On the other hand, in digital electronic printers it is known to conduct trapping in real time. However, the trapping here occurs at the bitmap level here, wherein limited information regarding the objects is made accessible to the trapping at the bitmap level by means of edge lists or shape directories.
It has previously been assumed that trapping at the object level could not be implemented in real time in a digital printing machine since a user cannot interactively affect the trapping in the plurality of different rules, and the trapping at the object level generates such a large volume of files that cannot be processed in real time.
Electrophotographic high-capacity printing systems are often components of digital production printing environments in which the pre- and post-processing of printed media is executed with automatic control. The document data are transmitted between the individual workstations in the form of document data streams in such production printing environments.
Different print data streams and printing systems that are suitable for processing the most varied print data streams (including AFP and IPDS) are described in the aforementioned publication “The World of Printers”, Dr. Gerd Goldmann (Editor), Océ Printing Systems GmbH, Poing, 7th edition (November 2002), ISBN 2-00-001019-X. In addition to this the print server system Océ PRISMAproduction is described in Chapter 14 (pages 343 to 361), for example. This flexible print data server system is suitable to, for example, receive print data from data sources such as a source computer—the print data being in a specific print data language such as AFP (Advanced Function Presentation), MO:DCA, PCL (Printer Command Language), PostScript, SPDS (Siemens Print Data Stream), in the Portable Document Format (PDF) developed by Adobe Systems Inc. or in the Line Coded Document Data Stream (LCDS) language developed by Xerox Corporation; to convert it into a specific output format—for example into the Intelligent Printer Data Stream (IPDS) format; and to transfer the data in this uniform output format to a print production system. Various technologies for color printing are described in Chapter 10.
In the specification and development of print data streams, the problem sometimes exists that new commands must be inserted into the data stream in order to take into account the technical developments of computers, printing apparatuses and/or post-processing apparatuses. The determination of such extensions is for the most part a relatively complicated process in which various industry partners must cooperate in order to agree on the changes or improvements among one another.
How three new data stream commands (namely WOCC, WOC and END) are added to the Intelligent Printer Datastream™ (IPDS™) is described in U.S. Pat. No. 6,097,498.
An additional possibility to store additional control data in an AFP data stream is to store data in what are known as object containers; see for example pages 93-95 in publication Nr. SC31-6802-05.
Additional techniques to insert new control information into AFP or IPDS data streams is described in WO 03/069548, originating from the assignee OCE Printing Systems GmbH.
How document objects such as text, images, graphics, barcodes and fonts are handled in the AFP and IPDS data streams is described in the IBM publication SC31-6804-05 with the title “Image Object Architecture Reference”, 6th Edition (August 2002). For this what is known as an Object Content Architecture (OCA) is defined in which specific data structures and control parameters or parameters characterizing the objects are defined for the respective objects, for example what is known as the Image Object Content Architecture (IOCA) for images, a corresponding GOCA for graphics, a PTOCA for presentation texts etc. The IOCA is described in detail in the aforementioned document. Additional IBM documents helpful in understanding the data streams are cited on pages v through vii of the document.
Details of the document data stream AFP™ are described in Publication Nr. F-544-3884-01, published by International Business Machines Corp. (IBM) with the title “AFP Programming Guide and Line Data Reference”. The document data stream AFP was further developed into the document data stream MO:DCA™ which, for example, is described in the IBM publication SC31-6802-06 (January 2004) with the title “Mixed Object Document Content Architecture Reference”. Details of this data stream are also described in U.S. Pat. No. 6,768,488. There specific field definitions of the data stream that contain control data (what are known as “structures fields”) are also explained.
AFP/MO:DCA data streams are frequently converted into data streams of the Intelligent Printer Data Stream™ (IPDS™) in the course of print production jobs. Such a process is shown in U.S. Pat. No. 5,982,997. Details regarding IPDS data streams are described in the IBM document Nr. S544-3417-06, “Intelligent Printer Data Stream Reference”, 7th Edition (November 2002), for example.
IPDS and AFP data streams normally contain and/or reference what are known as resources that contain data that are required to output the documents. Via simple referencing the data of a resource can thereby contain be used multiple times for one or more print jobs that in turn contain multiple documents or document parts, without having to be transferred multiple times. The amount of data to be transferred from a processing unit (for example a host computer generating the documents) to a subsequent processing unit (for example a print server or a printing apparatus) is thereby reduced, in particular when data of a plurality of documents that possess or require the same data in part are to be transferred. Examples of such resources are character sets (fonts) or forms to be overlaid with documents (overlays). The resources can thereby be contained in the document data stream itself or be transferred separate from this between the participating systems and can respectively only be referenced within different documents. It can thereby in particular be provided that the resources are already stored in an apparatus conducting additional processing (for example print server or printing apparatus) so that they do not need to be retransferred with every print job but rather must only be referenced.
In the presentation of AFP document data, resources that are present at various points in the AFP document data stream or originate from various sources are merged with the corresponding variable data of the documents, for example data for invoices that originate from databases, for example billing address, billing number, billing amount etc. The resource data can thereby be integrated into the document data stream as internal resources or be called from libraries as external resources via a resource name. Furthermore, the data are checked for consistency in a parsing process.
Details of how what is known as a line data or MO:DCA document data stream is converted into an IPDS data stream are described in the document “Print Services Facility for OS/390 & z/OS, Introduction”, Vers. 3, Release 3.0 Nr. G544-5625-03, March 2002 from IBM. The software program Print Service Facility (PSF) thereby combines variable document data with resource data in order to administer and control output data that are sent to a printer as an output apparatus. Software products under the trade names Océ SPS and Océ CIS that possess corresponding functions are developed and distributed by the applicant.
A method for secure administration and association of resources in the handling of resource-based print jobs is known from US 2005/0024668 A1. A method for processing resource data in a document data stream is known from WO-A1-2004/0008379.
Method for color reproduction in offset printing machines are known from Stollnitz J. et al., “Reproducing Color Images Using Custom Inks”, ACM Proceedings of the 25th annual conference on Computer graphics and interactive techniques, SIGGRAPH '98, ACM Press, July 1998.
The publications or documents and patent applications cited further above are herewith incorporated by reference into the present specification, and the methods, systems and measures described there can be applied in connection with the preferred embodiment.